Extranodal marginal zone B-cell lymphoma of the mucosa-associated lymphoid tissue (MALT) accounts for 7- 8% of all non-Hodgkin lymphomas. This tumor arises in sites that are normally devoid of lymphoid tissue, but which acquire organized lymphoid tissue as a result of chronic inflammation prior to the onset of lymphoma. The recurrent chromosomal translocation t(11;18)(q21;q21) occurs in up to 40% of cases and is associated with treatment resistance and tendency to disseminate. This translocation results in the creation of a chimeric protein composed of amino terminal sequences of Inhibitor of Apoptosis 2 (API2) fused to carboxy terminal sequences of MALT1. Despite strong evidence for an important role for t(11;18) in MALT lymphomagenesis, the molecular mechanisms underlying API2-MALT1's oncogenic activity have not been defined. The studies described in this proposal are aimed at elucidating the role of the API2 moiety in API2-MALT1-dependent oncogenic activity. We hypothesize that the API2 moiety of API2-MALT1 contributes to oncogenesis by mediating oligomerization of the fusion protein and by interacting with critical signaling proteins that regulate cell survival. We will use a combination of biochemical studies, cellular transformation analyses and mouse models to test this hypothesis. This research will further our understanding of the complex relationship between inflammation and cancer. The anticipated results will provide significant insight into the molecular pathogenesis of MALT lymphoma and will pave the way toward the development of novel rational therapies for refractory disease.